Ventilated filter tip cigarettes are well known and have been utilized for a number of years as a means for allowing air to be drawn into the cigarette during puffing which bypasses the burning zone and mixes with the smoke, thereby resulting in a cooler, less harsh-tasting cigarette. While a variety of ventilation techniques have been employed over the years, the most common practice has been to perforate the cigarette tipping paper with relatively small holes in a circumferential band or pattern around the cigarette mouthpiece, thereby providing openings for air to mix with the smoke as it is drawn through the cigarette. Such tipping paper is usually mechanically perforated and is used as an envelope over a uniformly porous plug wrap which encloses the filter plug whereby the air passes through the holes and the porous plug wrap into the filter media and mixes with the smoke from the cigarette. Typical cigarettes of this construction are disclosed in U.S. Pat. No. 2,988,088.
In recent years, more sophisticated ventilation techniques have been developed in which the filter plug is wrapped with a uniformly porous plug wrap and overwrapped with a uniformly porous tipping envelope. The tipping envelope and plug wrap are adhered together by an adhesive along preselected portions of their contiguous surfaces with the remaining portions left adhesive-free to allow air to pass through such areas and into the filter media to blend with the smoke. Such adhesive-free areas are generally referred to as ventilation regions. Cigarettes of this type of construction are disclosed in U.S. Pat. Nos. 3,805,800, 3,924,643 and 4,035,220.
One of the problems associated with cigarettes utilizing such porous tipping papers is variation in porosity or air permeability of the tipping paper causing large variations in pressure drop in cigarettes made therefrom resulting in inconsistent tar and nicotine yields from one cigarette to another in the same batch. The primary reason for the variation is the lack of uniformity in porosity of the inherently porous tipping papers. Such tipping papers are made on the paper machine with a relatively open structure so that air can readily pass through the paper. Due to the very nature of the paper manufacturing operation, it is very difficult to produce a consistent product having the same porosity on the machine during a run and especially from one run to the next.
Porosity control is very important with inherently porous tipping paper since the porosity of the product determines, to a large extent, the amount of air dilution obtained in cigarettes in which the paper is employed. Since such papers must be totally or partially printed for appearance purposes, this also has a pronounced effect upon porosity variation. Inherently porous tipping is overprinted with a solid or patterned design in order to impart increased light opacity to the porous sheet and give it standard tipping appearance, such as in the case of white tipping or cork tipping. Normally, the paper is printed using conventional rotogravure printing techniques to achieve good appearance in the finished printed product. If the rotogravure printing operation is performed in the normal manner by adjusting ink viscosity to give good appearance, the porosity of the printed tipping paper varies directly in accordance with variations in the porosity of the base paper. Moreover, it has been found that variations in porosity of the printed product are even greater than the variations in porosity in the base paper when conventional printing techniques are used. Therefore, it is an object of this invention to provide a method for producing printed inherently porous cigarette tipping papers in which the porosity of the printed product is controlled to obtain uniform porosity.